WHIP is also an unofficial
baseball statistic for
pitchers, and is an
abbreviation for
Walks plus
Hits over
Innings
Pitched.
The name is self-explanatory. To calculate WHIP, add a pitcher's hits and walks and divide this total by his innings pitched.
While the older and more common ERA (earned run average) stat measures the amount of runs a pitcher surrenders, WHIP measures the amount of baserunners.
For reference sake, a great WHIP ratio would be close to 1.0 (Pedro Martinez had the best WHIP in 2002, with 0.92; Randy Johnson's 1.01 led the Major Leagues in 2001). A more average WHIP is closer to around 1.3.
While ERA can be drastically affected by the size of a team's ballpark, WHIP is (arguably) a more consistent judge of a pitcher's worth.
WHIP is not a mainstream stat and you likely won't hear it in television broadcasts or similar. However, it's increasingly popular amongst stats junkies (SABRmetricians). It's also a common category used in fantasy baseball or rotisserie baseball.